Formation of an optically thick shocked shell in the very fast nova V1674 Herculis: the origin of superbrightness
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2025
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| _version_ | 1866909974587768832 |
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| author | Hachisu, Izumi Kato, Maiko |
| author_facet | Hachisu, Izumi Kato, Maiko |
| contents | V1674 Her is the fastest ($t_2\sim 1$ day) classical nova in our Galaxy and its absolute $V$ peak of $M_{V,\rm max}\sim -10.2$ is one magnitude brighter than typical very fast novae. Such a nova is sometimes called a superbright nova. Using our fully self-consistent nova outburst model combined with the optically thick winds on a $1.35 ~M_\odot$ white dwarf (WD) with a mass accretion rate of $1\times 10^{-11} ~M_\odot$ yr$^{-1}$, we have clarified that a strong reverse shock arises $0.3$ days after the outburst, which is just after the maximum expansion of the WD photosphere. The shocked shell is optically thick and expanding with the velocity of $\sim 3500$ km~s$^{-1}$. Its $V$ brightness reaches maximum of $M_{V,\rm max}=-10.2$ when the shocked shell expands to $R_{\rm shell}\sim 300 ~R_\odot$ on day $\sim 0.7$. After that, the shocked shell turns to optically thin and becomes fainter than the brightness of free-free emission from the nova wind. In chronological order, the optical brightness of free-free emission reaches maximum of $M_V=-9$ on day 0.3. However, it is overtaken on day 0.5--0.7 by the $\sim$1 mag brighter luminosity of the optically thick shocked shell. The GeV gamma-ray flux reaches maximum on day 0.4 because the gamma-rays are emitted by the shock that arises on day 0.3. Our model consistently explains both the superbrightness and chronological order that the gamma-ray peak precedes substantially before the optical $V$ peak. We also present a similar light curve model for another superbright nova V1500 Cyg. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_20175 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Formation of an optically thick shocked shell in the very fast nova V1674 Herculis: the origin of superbrightness Hachisu, Izumi Kato, Maiko Solar and Stellar Astrophysics High Energy Astrophysical Phenomena V1674 Her is the fastest ($t_2\sim 1$ day) classical nova in our Galaxy and its absolute $V$ peak of $M_{V,\rm max}\sim -10.2$ is one magnitude brighter than typical very fast novae. Such a nova is sometimes called a superbright nova. Using our fully self-consistent nova outburst model combined with the optically thick winds on a $1.35 ~M_\odot$ white dwarf (WD) with a mass accretion rate of $1\times 10^{-11} ~M_\odot$ yr$^{-1}$, we have clarified that a strong reverse shock arises $0.3$ days after the outburst, which is just after the maximum expansion of the WD photosphere. The shocked shell is optically thick and expanding with the velocity of $\sim 3500$ km~s$^{-1}$. Its $V$ brightness reaches maximum of $M_{V,\rm max}=-10.2$ when the shocked shell expands to $R_{\rm shell}\sim 300 ~R_\odot$ on day $\sim 0.7$. After that, the shocked shell turns to optically thin and becomes fainter than the brightness of free-free emission from the nova wind. In chronological order, the optical brightness of free-free emission reaches maximum of $M_V=-9$ on day 0.3. However, it is overtaken on day 0.5--0.7 by the $\sim$1 mag brighter luminosity of the optically thick shocked shell. The GeV gamma-ray flux reaches maximum on day 0.4 because the gamma-rays are emitted by the shock that arises on day 0.3. Our model consistently explains both the superbrightness and chronological order that the gamma-ray peak precedes substantially before the optical $V$ peak. We also present a similar light curve model for another superbright nova V1500 Cyg. |
| title | Formation of an optically thick shocked shell in the very fast nova V1674 Herculis: the origin of superbrightness |
| topic | Solar and Stellar Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2512.20175 |